1. Field of the Invention
The present invention relates to a deoxidizer in the form of a sheet (referred to as "deoxidizer sheet" hereinafter) for avoiding rottenness, degeneration or degradation of the foods.
2. Description of the Related Art
Deoxidizers are conveniently used in storing foods, particularly processed foods, because of their superior properties for preventing oxidation degradation, and generation of mildew and microaerobions.
Deoxidizers conventionally used for the purpose of storing foods are prepared in the form of powders or particles charged in small sacks made of air-permeable materials. A sack charged with the powder of a deoxidizer often has an appearance resembling that of a food package, causing a risk for the purchaser to dangerously eat the deoxidizer. A deoxidizer sack found in a mass of food sometimes imparts unpleasantness or suspicion to the purchaser. In addition, a sack of deoxidizer, when packaged together with foods in a package made of a gas-barrier material, impairs the appearance of the food package as a commercial product due to irregularity of the thickness of the sack.
Various sheet-type deoxidizers have been proposed to overcome the above-described problems of the deoxidizer sacks charged with powdered deoxidizers. For instance, Japanese Patent Unexamined Publication No. 54-114585 discloses a sheet-type deoxidizer formed by coating a sheet of a plastic or paper with a coating material in which a deoxidizer composition is blended. Japanese Patent
Unexamined Publication No. 55-44344 discloses a sheet formed from a blend of a deoxidizer composition and a thermoplastic resin. A sheet-type deoxidizer disclosed in Japanese Patent Unexamined Publication No. 56-26524 is produced by forming a sheet from a blend of a deoxidizer composition and a foamable resin and then allowing the resin to foam. In Japanese Utility Model Unexamined Publication No. 60-10768, a deoxidizer composition is sprayed on an adhesive layer which coats a base sheet. Japanese Patent Unexamined Publication No. 55-106519 discloses a sheet-type deoxidizer which is formed by applying an adhesive to a fibrous sheet, dispersing a deoxidizer composition in the fibrous sheet, and bonding this fibrous sheet to another fibrous sheet to which the same adhesive is applied. Japanese Patent Unexamined Publication No. 55-109428 discloses a sheet-type deoxidizer having a deoxidizer layer composed of a porous layer with its pores filled with a deoxidizer composition.
These known sheet-type deoxidizers, however, suffer from various disadvantages. For instance, a sheet formed from a blend of a coating resin material and a deoxidizer composition, even when it is of foamed type, encounters a problem in that the oxygen absorption performance is limited so that the deoxidizing rate is small and oxygen absorption capacity is also small as compared with a conventional deoxidizer charged in a gas-permeable sack. The sheet-type deoxidizer produced by spraying a deoxidizer composition on an adhesive layer also is disadvantageous in that the oxygen absorption capacity per unit area is impractically small because of too small a quantity of composition carried by the adhesive layer. The sheet-type deoxidizer having a porous base sheet suffers from the following disadvantage, particularly when iron powder is used as the deoxidizer which fills the pores. Namely, the iron powder tends to be concentrated to the bottoms of the pores in the porous base sheet due to its large specific weight so that it is difficult to uniformly disperse the iron powder even if a fibrous sheet having mingling fibers such as a non-woven cloth is used as the porous base sheet. In addition, it is difficult to fix the deoxidizer composition in this type of sheet. For these reasons, problems are often experienced such as scattering of the deoxidizer powder from a cut edge of the sheet and easy separation of the outer film.